A target detection method under the influence of a sheath based on a distance-doppler two-dimensional ambiguity function

Abstract

The present application relates to the field of radar, and is a target detection method and system under the influence of sheath based on range-doppler two-dimensional ambiguity function. It includes the following steps: according to the radar echo signal peak value, screening a plurality of scattering points of target surface plasma sheath; transmitting radar signals using linear frequency modulation (LFM) signals, and establishing a LFM signal echo model of the plasma sheath covering target according to the screened scattering points; analyzing the range-doppler two-dimensional ambiguity function diagram of the echo signal of the LFM signal echo model, distinguishing the sheath target from the real target, and realizing target detection under the influence of sheath. The present application makes two-dimensional ambiguity function of echo signal, analyzes the range-doppler two-dimensional ambiguity function diagram of radar echo, distinguishes the sheath target and the real target and other general targets through the characteristics of ambiguity function diagram, and realizes stable recognition and tracking of targets.

Description

Technical Field

[0001] This invention relates to the field of radar, and in particular to a target detection method and system based on the influence of the sheath under the range-Doppler two-dimensional ambiguity function. Background Technology

[0002] When a radar-detected target passes through the Earth's atmosphere at high speed, collisions between molecules in the atmosphere cause ionization of molecules or atoms. The degree of ionization increases rapidly with rising temperature, resulting in thermal ionization. The thermally ionized molecules and atoms coat the surface of the target, forming a high-temperature plasma layer surrounding the target aircraft, also known as a plasma sheath.

[0003] During radar target detection, the plasma sheath not only causes electromagnetic interference to the target echo but also reflects the radar signal, increasing the signal components in the target echo and resulting in a signal with rich Doppler frequency components. The Doppler components generated by the plasma sheath are complex, and their absolute values ​​are smaller than the target's Doppler. Due to the range-Doppler coupling effect during pulse compression of linear frequency modulated signals, the radar echo signal contaminated by the sheath exhibits a "sheath target" phenomenon in the radar's one-dimensional Doppler spectrum, severely affecting target detection. Because of the time-varying range difference between the sheath target and the real target, and because the sheath target is often distributed across several range cells within a certain range, and even worse, sometimes the spectral peak of the sheath target may be larger than that of the real target, this leads to significant difficulties in radar target identification, unstable target tracking, poor tracking accuracy, and even loop lock-out problems.

[0004] In a one-dimensional Doppler radar spectrum, the positions of the reflected echo spectra of the real target and the sheathed target differ. Besides the spectral peak corresponding to the reflected echo of the real target, there is also the spectrum of the reflected echo from the sheathed target. When there are accompanying targets around the real target, the echo signal received by the radar, after pulse compression processing, will also face interference from the spectrum of the sheathed target. It is difficult to distinguish between the real target and the sheathed target solely from the signal spectrum after pulse compression processing, easily leading to inaccurate radar target identification. Summary of the Invention

[0005] To address the problems in existing technologies, this invention proposes a target detection method and system based on a range-Doppler two-dimensional ambiguity function under the influence of sheaths. The radar transmits an LFM (Linear Frequency Modulation) signal. After receiving the echo signal, a two-dimensional ambiguity function is applied to the echo, and the range-Doppler two-dimensional ambiguity function graph of the radar echo is analyzed. By utilizing the characteristics of the ambiguity function graph, sheath targets and general targets such as real targets can be distinguished, thereby achieving robust target identification and tracking.

[0006] The target detection method of this invention adopts the following technical solution: a target detection method based on the sheath effect of the distance-Doppler two-dimensional ambiguity function, comprising the following steps:

[0007] Step 1: Based on the peak value of the radar echo signal, select several scattering points of the plasma sheath on the target surface;

[0008] Step 2: Transmit radar signals using linear frequency modulated (LFM) signals, and establish an LFM signal echo model of the target covered by the plasma sheath based on the selected scattering points.

[0009] Step 3: Analyze the distance-Doppler two-dimensional fuzzy function graph of the echo signal of the LFM signal echo model to distinguish the sheath target from the real target and realize target detection under the influence of the sheath.

[0010] The technical solution adopted by the target detection system of this invention is as follows: a target detection system based on the sheath effect of the range-Doppler two-dimensional ambiguity function, comprising the following modules:

[0011] The scattering point screening module is used to screen several scattering points of the plasma sheath on the target surface based on the peak value of the radar echo signal.

[0012] The echo model construction module uses linear frequency modulated (LFM) signals to transmit radar signals and establishes an LFM signal echo model of a target covered by a plasma sheath based on several selected scattering points.

[0013] The detection module analyzes the distance-Doppler two-dimensional fuzzy function graph of the echo signal of the LFM signal echo model to distinguish the sheath target from the real target, thus realizing target detection under the influence of the sheath.

[0014] Compared with the prior art, the technical effects achieved by the present invention include:

[0015] In the target detection process, the radar uses a linear frequency modulated (LFM) signal as the detection waveform and transmits a series of signal pulses. A two-dimensional fuzzy function is applied to the signal echo, and the radar echo range-Doppler two-dimensional fuzzy function graph is analyzed. Through the characteristics of the fuzzy function graph, sheath targets and general targets (such as real targets and escort targets) are distinguished, thereby achieving robust target identification and tracking. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a plasma sheath for radar target detection in an embodiment of the present invention;

[0017] Figure 2 This is a flowchart of the target detection method provided in the embodiments of the present invention;

[0018] Figure 3 This is a schematic diagram of the relationship between carrier frequency and frequency modulation slope in an embodiment of the present invention, wherein (a) is a schematic diagram of up-modulated LFM signal and (b) is a schematic diagram of down-modulated LFM signal;

[0019] Figure 4 This is a fuzzy function graph of the LFM signal in an embodiment of the present invention;

[0020] Figure 5 This is a schematic diagram of the distance-Doppler two-dimensional ambiguity function between the real target and the accompanying target in an embodiment of the present invention;

[0021] Figure 6 This is a schematic diagram of the distance-Doppler two-dimensional fuzzy function between the real target and the sheath target in an embodiment of the present invention. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0023] Example 1

[0024] This embodiment provides a target detection method based on the range-Doppler two-dimensional ambiguity function under the influence of the plasma sheath. Before describing the specific implementation steps of this embodiment, the formation principle of the plasma sheath is introduced as follows:

[0025] Radar uses electromagnetic waves to detect targets. It emits electromagnetic waves to the target and receives the echoes, thereby obtaining information such as the distance, speed, azimuth, and altitude of the target from the radar's electromagnetic wave emission point. When a target passes through the Earth's atmosphere at high speed, collisions between molecules in the atmosphere cause ionization of molecules or atoms, and the degree of ionization increases rapidly with increasing temperature, resulting in thermal ionization. The thermally ionized molecules and atoms cover the target's surface, forming a high-temperature plasma layer surrounding the target aircraft, also known as a plasma sheath. This plasma sheath layer formed on the surface of a high-speed reentry vehicle upon atmospheric reentry has a significant impact on the vehicle's communication, flight control, and tracking, preventing normal radar detection. Throughout the radar detection process of a reentry target, at a certain altitude range through the atmosphere, the target surface is covered by a plasma sheath. Therefore, in the case of coupling between fluid and rigid bodies, the target exhibits complex echo reflection points on its sheath layer in addition to the main target itself. Figure 1As shown, the gray area in the middle represents the reentry target (i.e., the real target, also called the target body) itself, and the black dots above it represent scattering points at different locations on the sheath layer on the surface of the reentry target. Plasma is generated at these scattering points and flows towards the tail of the target, forming a plasma sheath layer. When the reentry target moves to a certain altitude, the plasma sheath layer formed on the target surface approaches a stable state.

[0026] like Figure 2 As shown, the target detection method based on the distance-Doppler two-dimensional ambiguity function under the influence of the sheath provided in this embodiment specifically includes the following steps:

[0027] Step 1: Based on the peak value of the radar echo signal, select several scattering points of the plasma sheath on the target surface.

[0028] During the entire process of detecting the target using this embodiment, when the target passes through a certain altitude range of the atmosphere, the target surface will be covered with a plasma sheath. For example... Figure 1 As shown, in this embodiment, black dots are used to mark scattering points at different locations on the plasma sheath layer (hereinafter referred to as the sheath target) on the surface of the target body (hereinafter referred to as the real target). Plasma is generated at these scattering points and flows towards the tail of the target, forming a plasma sheath layer. When the target moves to a certain height, the plasma sheath layer formed on the target surface approaches a stable state.

[0029] In this embodiment, plasma with a scattering intensity greater than a preset threshold is generated at the selected scattering points and flows towards the tail of the target. The preset threshold can be specifically set according to the actual application.

[0030] Step 2: Transmit radar signals using linear frequency modulation (LFM) signals, and establish an LFM signal echo model of the target covered by the plasma sheath based on the selected scattering points.

[0031] The LFM signal transmitted by the radar can be represented as:

[0032]

[0033] Among them, f c f is the carrier frequency of the LFM signal. d Here, k = B / T is the Doppler frequency, B is the frequency modulation slope, and T is the pulse period; rect(t / T) represents a rectangular signal.

[0034]

[0035] A schematic diagram illustrating the relationship between carrier frequency and frequency modulation slope is shown below. Figure 3As shown, sub-figure (a) is a schematic diagram of an up-modulated LFM signal, and sub-figure (b) is a schematic diagram of a down-modulated LFM signal. In the figure, f0 is the center frequency.

[0036] The echo signal received by the radar can be represented as:

[0037]

[0038] Where, τ i The time delay of the echo signals received by the radar antenna from different scattering points is represented by , i represents the selected main target and different scattering points on the plasma sheath, and k represents the frequency modulation slope.

[0039] The ambiguity function of the LFM signal can be expressed as:

[0040]

[0041] And:

[0042]

[0043] Where τ0 represents the pulse width. The ambiguity function graph of the LFM signal is shown below. Figure 4 As shown.

[0044] Step 3: Analyze the distance-Doppler two-dimensional fuzzy function graph of the echo signal of the LFM signal echo model to distinguish between sheath targets and general targets such as real targets, and realize target detection under the influence of sheath.

[0045] The echo signal received by the radar includes echoes reflected from general targets such as real targets and escort targets, as well as echoes reflected from sheath targets. This step analyzes the range-Doppler two-dimensional ambiguity function graph of the echo signal to distinguish sheath targets from general targets such as real targets and escort targets.

[0046] Assume that at time t0, the real target is located at a distance R0 from the radar. Near R0, there will be sheath target scattering points due to the presence of the plasma sheath. These scattering points are approximately equidistant from the radar at R0, but their velocities differ from those of the real target. Also, assume there is a reference target at a distance R0 from the radar, and that this target is stationary, i.e., its velocity is zero. From the Doppler frequency calculation formula, the Doppler frequency between the real target and the reference target is:

[0047]

[0048] Where v0 is the velocity of the real target.

[0049] In real-world target identification scenarios, the spectrum of the echo reflected from a sheathed target may be dense and have a large amplitude, making it difficult for the radar to distinguish between the real target and the sheathed target in the echo signal. This embodiment plots a range-Doppler two-dimensional ambiguity function on the radar-received echo to analyze its characteristics. The range-Doppler two-dimensional ambiguity function plots for the real target and the accompanying target (i.e., general target) are shown below. Figure 5 As shown in the figure, the distance-Doppler blur function graph of the real target and the group of accompanying targets flying together exhibits several independent peak-shaped random distributions.

[0050] Distance between the real target and the sheath target - Doppler two-dimensional ambiguity function as follows Figure 6 As shown in the figure, the distance-Doppler two-dimensional fuzzy function graph of the sheath target is distributed in a "sheath ridge" shape, that is, multiple peaks in the fuzzy function graph are arranged regularly, for example, arranged in a regular column.

[0051] In practical radar target detection scenarios, if the range-Doppler two-dimensional ambiguity function graph of the echo signal exhibits a sharp, independent peak distribution, it is identified as a real target; if the range-Doppler two-dimensional ambiguity function graph of the echo signal exhibits a "sheath ridge" distribution, it is identified as a sheathed target. By analyzing the characteristics of the target's echo range-Doppler two-dimensional ambiguity function graph, sheathed targets and real targets can be distinguished, achieving robust target identification and tracking.

[0052] Example 2

[0053] This embodiment is based on the same inventive concept as Embodiment 1, and provides a target detection system under the influence of sheath based on the distance-Doppler two-dimensional ambiguity function, specifically including the following modules:

[0054] The scattering point screening module is used to screen several scattering points of the plasma sheath on the target surface based on the peak value of the radar echo signal.

[0055] The echo model construction module uses linear frequency modulated (LFM) signals to transmit radar signals and establishes an LFM signal echo model of a target covered by a plasma sheath based on several selected scattering points.

[0056] The detection module analyzes the distance-Doppler two-dimensional fuzzy function graph of the echo signal of the LFM signal echo model to distinguish the sheath target from the real target, thus realizing target detection under the influence of the sheath.

[0057] In this embodiment, the LFM signal transmitted by the radar is represented as:

[0058]

[0059] Among them, f c f is the carrier frequency of the LFM signal. dHere, k is the Doppler frequency, k = B / T is the frequency modulation slope, B is the bandwidth, and T is the pulse period; rect(t / T) is a rectangular signal.

[0060] The echo signal received by the radar is represented as:

[0061]

[0062] Where, τ i The time delay of the echo signal received by the radar antenna from different scattering points is represented by , and i represents the different scattering points selected.

[0063] In practical radar target detection scenarios, the detection module distinguishes between sheath targets and real targets by: if the range-Doppler two-dimensional fuzzy function graph of the echo signal shows a random and independent distribution of sharp peaks, it is determined to be a real target; if multiple peaks in the range-Doppler two-dimensional fuzzy function graph of the echo signal are regularly arranged, it is determined to be a sheath target. By analyzing the characteristics of the target's echo range-Doppler two-dimensional fuzzy function graph, sheath targets and real targets are distinguished, achieving robust target identification and tracking.

[0064] Each module in this embodiment is used to implement the corresponding steps in embodiment 1. The detailed implementation process can be found in embodiment 1, and will not be repeated here.

[0065] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A target detection method based on the sheath effect of a distance-Doppler two-dimensional ambiguity function, characterized in that, Includes the following steps: Step 1: Based on the peak value of the radar echo signal, select several scattering points of the plasma sheath on the target surface; Step 2: Transmit radar signals using linear frequency modulated (LFM) signals, and establish an LFM signal echo model of the target covered by the plasma sheath based on the selected scattering points. Step 3: Analyze the distance-Doppler two-dimensional fuzzy function diagram of the echo signal of the LFM signal echo model to distinguish between the sheath target and the real target, and realize target detection under the influence of the sheath; The echo signal received by the radar in step two is represented as follows: ； in, The carrier frequency of the LFM signal. For Doppler frequency, This indicates the time delay of the echo signals received by the radar antenna from different scattering points. This indicates the different scattering points selected. Indicates the frequency modulation slope; Step three, which distinguishes between sheath targets and real targets, includes: If the range-Doppler two-dimensional fuzzy function graph of the echo signal shows a peak-shaped random independent distribution, it is determined to be a real target; if multiple peaks are regularly arranged in the range-Doppler two-dimensional fuzzy function graph of the echo signal, it is determined to be a sheath target. The echo signal has multiple spikes arranged regularly in a column in the distance-Doppler two-dimensional ambiguity function graph.

2. The target detection method according to claim 1, characterized in that, At the selected scattering points, plasma with a scattering intensity greater than a preset threshold is generated and flows toward the tail of the target.

3. The target detection method according to claim 1, characterized in that, The LFM signal transmitted by the radar in step two is represented as follows: ； in, The carrier frequency of the LFM signal. For Doppler frequency, For frequency modulation slope, For bandwidth, The pulse period; It is a rectangular signal.

4. The target detection method according to claim 1, characterized in that, The ambiguity function of the LFM signal in step two is: ； And: ； in, Indicates the pulse width. For Doppler frequency, This indicates the frequency modulation slope.

5. A target detection system based on the sheath effect of a range-Doppler two-dimensional ambiguity function, characterized in that, Includes the following modules: The scattering point screening module is used to screen several scattering points of the plasma sheath on the target surface based on the peak value of the radar echo signal. The echo model construction module uses linear frequency modulated (LFM) signals to transmit radar signals and establishes an LFM signal echo model of a target covered by a plasma sheath based on several selected scattering points. The detection module analyzes the distance-Doppler two-dimensional fuzzy function graph of the echo signal of the LFM signal echo model to distinguish the sheath target from the real target, thus realizing target detection under the influence of the sheath. The echo signal received by the radar is represented as: ； in, The carrier frequency of the LFM signal. For Doppler frequency, This indicates the time delay of the echo signals received by the radar antenna from different scattering points. This indicates the different scattering points selected. Indicates the frequency modulation slope; The process by which the detection module distinguishes between sheath targets and real targets includes: If the range-Doppler two-dimensional fuzzy function graph of the echo signal shows a peak-shaped random independent distribution, it is determined to be a real target; if multiple peaks are regularly arranged in the range-Doppler two-dimensional fuzzy function graph of the echo signal, it is determined to be a sheath target. The echo signal has multiple spikes arranged regularly in a column in the distance-Doppler two-dimensional ambiguity function graph.

6. The target detection system according to claim 5, characterized in that, The LFM signal transmitted by the radar is represented as: ； in, For frequency modulation slope, For bandwidth, The pulse period; It is a rectangular signal.

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